The purine salvage enzyme adenine phosphoribosyl transferase, (APRT) from rat liver and human red blood cells has been purified to homogeneity by affinity chromatography. Antibody has been prepared to the purified enzyme. At the same time a series of mutants of APRT have been isolated in Chinese hamster ovary cells. Utilizing affinity chromatography (AMP and antibody) we shall purify the CRM plus proteins, and analyze peptide maps of wild type and mutant proteins. This will allow us to examine the molecular effects of the mutagens used in this study, and to differentiate regulatory mutations from structural alterations. We shall form recombinants (in vitro) between CHO and SV-40 DNA, such recombinants will be used to transduce APRT minus CHO cells to APRT plus. Assumably this will involve integration of the viral genome. Clones transduced by SV-40 APRT plus will be hybridized to permissive cell lines, and screened for the production of viable APRT viruses. This DNA will then be used for enrichment as a source of genomic APRT DNA.